Famously private, Kennedy nonetheless emerged during the Obama campaign as a political force of her own. Along the way, friends and colleagues say, she discovered that she had a higher tolerance than she thought for public appearances and a long-dormant desire for public service.

Now, Kennedy, 51, the only surviving child of former president John F. Kennedy, is the front-runner to assume the Senate seat in New York once held by her uncle Robert F. Kennedy and soon to be relinquished by  Hillary Rodham Clinton.

Although there are other contenders for the job, establishment figures have quickly closed ranks around Kennedy. Yesterday,  Senate Majority Leader Harry M. Reid (D-Nev.) became the latest to voice his support for having New York Gov. David A. Paterson (D) appoint Kennedy to replace Clinton when she becomes Obama's secretary of state.

Trying to explain the political ambitions of Kennedy, who was sheltered from the glare of publicity after her father's assassination in 1963 and has rarely emerged from it since, several people close to her said yesterday that she had long expressed a desire for a more active public life.

Joel I. Klein, chancellor of the New York City Department of Education and a Kennedy confidant, said he had a conversation with her eight years ago in which "it seemed to me she was now ready to start moving back into the public sector." The Obama campaign, he said, "was obviously a major turning point," adding that it "probably surprised" Kennedy how much she enjoyed the campaigning.

"Certainly this year she's played a very significant role in the presidential campaign, and I think that has very much crystallized her interest in serving," said John Shattuck, chief executive of the John F. Kennedy Presidential Library Foundation in Boston, who has worked with her since 2001. "But this is something that's been a long time coming."

Most of the country has caught only occasional glimpses of Kennedy's evolution from a young girl, shielded by her mother after her father's death, to a poised, intellectual mother of three who is devoted to quiet reflection and philanthropic causes. Her life, led mostly in New York City, has been marked by her family's tragedies, including the death of her brother, John F. Kennedy Jr., in a plane crash in 1999, and her uncle  Edward M. Kennedy's battle with brain cancer.

A lawyer and the author of several books, Kennedy is perhaps most acclaimed for raising tens of millions in private money for the New York City school system. She works with multiple foundations, playing an active role in the Kennedy library and the Institute of Politics at Harvard University. She has dipped in and out of the public eye over the years; she was sometimes referred to by her married name, Schlossberg, and at other times just as Kennedy, which, an aide said yesterday, is what she prefers.

Although she has been an important symbol in Democratic politics throughout her life, and participated in tributes to the Kennedy family in earlier party conventions, it was not until the 2008 primaries that she exerted her own influence in a forceful way. On the heels of Obama's major victory in the South Carolina Democratic primary in late January, Kennedy added to his momentum in a way that would be unstoppable, declaring on the opinion pages of the New York Times: "I have never had a president who inspired me the way people tell me that my father inspired them." It was the first time she had endorsed a presidential candidate in the primaries since her uncle Ted ran in 1980.

During this year's primaries and the general-election campaign, Kennedy made some high-wattage appearances, including on NBC's "Meet the Press," alongside her cousin Maria Shriver, and at the Democratic National Convention. She shared the stage with Obama's wife, Michelle, at a Los Angeles rally that also included Oprah Winfrey.

But much of Kennedy's work was far more low-key. She worked phone banks and chatted up people on the street. One Obama adviser said she did not want the campaign to build large crowds for her events, instead hoping to blend in during small-scale appearances. "She liked getting her hands dirty and going and doing sort of basic work," the adviser said, speaking on the condition of anonymity because the president-elect has not formally weighed in on the New York Senate seat, although several members of his operation said yesterday that they are eager to see Kennedy get the job.